Thumbs.db is a hidden file generated automatically by Windows, you will see it in many folders if you have set the "Show hidden files and folders" option in the "Folder Options" window on. Although Windows mostly generates it to speed things up, some times it is annoying especially when you try to zip a folder or upload a folder using ftp to your site, I have found Thumbs.db in most of the folders in my site and had to delete them manually. If you delete Thumbs.db from your windows folders, Windows will generate it again when you re-open the folders if you have Filmstrip or Thumbnails selected in the View menu of those folders. If the Thumbs.db is considered annoying for you, there is an easy way to stop Windows from re-generating it, here is how.